1. Field of the Invention
The present invention relates to fuel cells and in particular to solid oxide fuel cells.
2. Discussion of Prior Art
Fuel cells are electrochemical devices that convert chemical energy obtained from the reactants into electrical energy. A number of different families of such devices have been developed in the prior art. These vary according to the type of electrolyte used in the cell and the usual temperature of operation. All of the deices burn fuel at the anode or negative electrode and consume an oxidant at the cathode or positive electrode. The present invention is concerned with so-called solid oxide fuel cells, herein called "SOFC s", in which the electrolyte is a solid refractory oxide, and a temperature of the order of 900 to 1000 C. is employed in operation of the cell. Such cells normally form one building block of a stack of cells of an electrochemical energy source.
In more known SOFCs the electrolyte is contained between an anode and a cathode and the anode and cathode of adjacent cells in a stack are contained between an interconnect or bipolar plate which permits electronic conduction and allows reactant gases to be delivered separately to regions adjacent to the anode and cathode. The reactant gases will generally comprise oxygen usually supped as air as oxidant and hydrogen or a hydrogen containing compound, e.g. methane, as fuel. The interconnect or bipolar plate needs to be gas impervious to keep the reactant gases separate as well as electrically conducting to permit transport of electrons to and from the electrode surfaces to facilitate the electrochemical processes. As a result, the designs of such cells in the prior art have involved for the interconnect the fabrication and use of materials such as lanthanum chromite which are very expensive. These interconnects have been manufactured in an expensive sandwich structure form to provide the necessary gas permeability barrier between suitably channeled gas transporting layers.
It is a purpose of the present invention to reduce the fabrication cost of such cells and stacks incorporating them.